Patent GB-574819-A (GB)
Title: Apparatus for testing the density of fluids
IPC: G01N29/036
Filed: 1943-08-20
Abstract: 574,819. Measuring density of fluids. BENDIX AVIATION CORPORATION. Aug. 20, 1943, No. 13577, Convention date, Aug. 1, 1942. [Classes 13, 40 (i) and 118 (ii)] [Also in Groups XXXIX and XL] The density of a fluid under test is made to control the frequency of an oscillation-generator and this frequency or a frequency derived by beating it with the output of a standard generator is measured or the frequency of the test oscillator is adjusted to a standard value and the amount of the adjustment is observed. As shown in Fig. 3, the feed-back path of a thermionic generator comprises a delay system formed by a transducer 2 for converting the oscillations generated into sound waves, a tube 41 containing the test fluid to which the sound waves are applied and a transducer 3 for reconverting the sound energy ;nto electric energy and a filter 6 for eliminating frequencies in the neighbourhood of the natural frequencies of the transducers unless these are made non- resonant, e.g. by a dashpot. In these circumstances, the frequency generated is that for which the passage of the sound wave through the tube gives a delay of (2n- 1)# with one relative arrangement of the connections of the transducers or 2n# with the other and so depends on the velocity of sound in, and thus on the density of the fluid concerned. The length of the tube may be varied by a temperature-sensitive device 33 to eliminate errors due to variations of the density of the fluid with temperature. In another arrangement, Fig. 4 (not shown), these errors are eliminated in a tube of fixed length by beating the oscillations with those generated by a similar oscillator in which the composition of the gas in the tube is fixed, both tubes being subject to the same variations of temperature and pressure. In a similar arrangement, Fig. 10 (not shown), the beat oscillations are detected by a telephone receiver and the length of the tube of the test oscillator is adjusted manually until they disappear ; the amount of the adjustment being observed. In another arrangement, Fig. 9, the frequency of a generator comprising a pair of reciprocally coupled tubes is determined by a tuned circuit shunted by a moving coil transducer acting on a column of the gas to be tested. The length of the tube is adjusted until this frequency is the same as that generated by a standard oscillator 86. The system can be used with recording frequency-meters for continuous monitoring and recording'of the specific gravity of boiler-water or petroleum distillates. Construction of electro-mechanical tranducers and delay system. The moving coil is carried by a former 19, Fig. 2, which is supported by a pair of spiders from the walls of the tube 1 and carries a plate 20. The permanent magnetic field is provided by a piece 23 of Alnico &c. An air-tight connection is made between the tube and the casing 27. Instead of a simple tube, the tube shown in Fig. 6, in which nodes are produced at the points 58, by means of side chambers containing absorbing material 57 such as rock wool or hair felt, may be used. The generated frequency is then three times what it would be with a simple tube. To make the moving system non- resonant, the coil-former may be connected to the plunger of a dashpot, Fig. 5 (not shown).